In the letter, seen by Australian media, Mr Macken said: “My reason for making this proposal is simple. I can no longer remain silent as innocent men, women and children are being held in appalling circumstances on Manus Island and Nauru.

“It is even worse that they are being held in these dangerous and inhospitable conditions in order to ensure no other asylum seekers and refugees attempt to come to Australia for protection.

“The Australian government is essentially treating refugees in these camps as human shields and this is utterly immoral. As this is being done in my name I cannot remain silent.

“I offer this proposal as a way forward for at least one refugee. This would allow one person currently held on Manus Island or Nauru the right to be an Australian citizen. I would consider it a privilege to live out my final years in either Nauru or Manus Island in his or her stead.”

Media captionLife in the Nauru detention centre

Mr Macken reportedly offered to relinquish his Australian citizenship if necessary.

A spokeswoman for Mr Dutton said the minister’s office was checking to see if it had received the letter, which was sent a month ago, and declined to comment further.

Mr Macken also wrote to Prime Minister Malcolm Turnbull and Labor party leader Bill Shorten, urging them to “err on the side of compassion and justice” and end offshore processing.

A spokesman for the prime minister declined to comment.

Speaking to the Guardian, Mr Macken said he had “nothing to lose” by making his offer.

“If it gets just one refugee off one of those islands, and gives them a chance at a life in Australia, I’m prepared to do it,” he said.

He said he wasn’t seeking publicity and would be happy to undertake the exchange without notifying the public.

Mr Macken was a barrister and union organiser until his retirement in 1989. He was appointed a member of the Order of Australia in 2003.

Australia and asylum

Image copyrightAmnesty InternationalImage caption A photo taken by Amnesty International shows the inside of a tent housing asylum seekers in Nauru

The number of asylum seekers travelling to Australia by boat rose sharply in 2012 and early 2013. Scores of people have died making the journey.

To stop the influx, the government adopted tough measures intended as a deterrent.

Everyone who arrives is detained. Under the policy, asylum seekers are processed offshore at centres on Nauru and Manus Island in Papua New Guinea.

The government has also adopted a policy of tow-backs, or turning boats around.